Who has ever made this claim? Please, show me, because I have never once heard it. Of course most individuals are physically capable of producing offspring. Natural selection is dependant upon which individuals will pass their genetic information on to the next generation, and that is determined by at least two factors that I can think of at the moment: 1.) An individual being able to survive long enough to find a mate, and 2.) Actually being able to find a mate and produce offspring, which brings me to my next point:
Label: Non-Sarcastic